how to judge there is content in QTextEdit in QT? - qt5

Question

I have written a notepad which looks like notepad in Windows. How to set to make the find action disabled when the QTextEdit empty but enabled when something in it

Answer 1

The myTextEdit->plainText().isEmpty() procedure does not seem to be very efficient: The plainText method needs to convert the full QTextEdit contents into a new QString buffer, which is expensive if the QTextEdit contains a large amount of text.
I suggest to use myTextEdit->document()->isEmpty() instead, which queries the QTextDocument storage, i.e. the original data structure.
In my use case, the QTextEdit contains an error log, and before appending a line I check if the text is empty; if not, I insert a newline(*). Converting the log buffer to a QString each time a line is appended would be a bad idea.
(*) I cannot insert a newline together with each log entry, because the entries themselves are comma-separated lists. Roughly speaking I have a newEntry(...) and a newLine(...) function, and newEntry does not know if newLine or newEntry will be called next.

Answer 2

You connect a function that enables/disables the action based on the text edits plainText(), to the textChanged() signal of the text edit.
For example:
void MyWidget::someSetupMethod()
{
// ... some code that sets up myTextEdit and myFindAction here
connect(myTextEdit, &QTextEdit::textChanged, myFindAction, [myTextEdit, myFindAction]() {
myFindAction->setEnabled(!myTextEdit->plainText().isEmpty());
});
// ...
}
or, if you cannot or do not want to use C++11, something like
void MyWidget::someSetupMethod()
{
// ... some code that sets up m_myTextEdit and m_myFindAction here
connect(m_myTextEdit, &QTextEdit::textChanged, this, &MyWidget::updateFindAction);
// ...
}
void MyWidget::updateFindAction()
{
m_myFindAction->setEnabled(!m_myTextEdit->plainText().isEmpty());
}